The aim of this project remains the study of regulatory mechanisms involved in normal cell differentiation and malignant transformation. The mouse melanoma (B16) model system used involves cells grown in culture with or without 5-bromodeoxyuridine (BrdU). Cell clones used are melanotic, tumorigenic B559; amelanotic, tumorigenic B78; and amelanotic, nontumorigenic, immunogenic C3471. B559 and B78 are grown in normal medium; C3471 is grown with BrdU (1 micron g/ml). We are studying the host response to inoculations of B559, C3471 separately and mixed. We are examining further the inhibition of plasminogen activator activity of B559 by C3471 and its relationship to the decreased tumorigenicity of mixtures. We have initiated a pilot study of nuclear-cytoplasmic interactions relating to differentiation and malignancy by means of somatic cell hybridization and cybridization. We are studying interactions of melanin-stimulating hormone with each cell type. We are characterizing the cell surface similarities and differences among the cell types biochemically by studying glycoproteins and glycosaminoglycans, by looking at isozymes and LETS protein. These varied lines of research should lead to further understanding of possible reasons for the differences in tumorigenicity and immunogenicity among these melanoma cell types and to further understanding of the regulation of melanogenisis.